No, Snell 2015 also expires at the end of 2023.. FIA from then on only..

...but all SNELL 2015 helmets meet the FIA standard as well, so logic dictates that particular FIA standard (8859-2015 is it?) will last about 5 years longer than the equivalent SNELL 2010 standard (8860-2010 is it?). I've just bought a 2015 helmet after I discovered my previous helmet wasn't the SNELL 2010 model I was told it was when I bought it.